Yet another DIY GPSDO - yes, another one

[daddioo]

Thanks for your answers, I connected a 15V 3A power supply, I made a small circuit with two transistors and two LEDs, one red that indicates heating and one green that indicates the RB is in Lock, I used Pin 3 Bit Lock, I put it in ON, the red LED immediately turned on, after about 5 minutes the green LED turned on, I connected an oscilloscope and I got 10Mhz and 2.5V peak to peak.
I tried to connect it to the GPSDO Project, connected in this way 10Mhz output to the 100 ohm resistor and Pin 8 (Freq. Adj) to the pwm dac unfortunately it does not work it always remains in Calibration, I was curious to see the Rubidium controlled by the GPSDO, if I connect the ocxo it works as you saw in the previous photo, then I tried to connect it to BG7TBL it works very well in 35/50 minutes it went into Lock, I do not understand in the AndrewBCN project it does not work.

[Johnny B Good]

Assuming the freq adj pin option is enabled, The tuning rate is likely to be in the region of 167 volts/Hz!

[EDIT]
 I'd missed the reference to the BG7TBL. If that's the rubidium version then you've proved that the freq adj pin is at least functioning and your problem is the totally mismatched tuning rates between the gpsdo project and the AR60A. Given enough time, the gpsdo may eventually finish re-calibrating itself to the rubidium oscillator's requirements.

 The total tuning range for each of the internal trimpot and the external C field connection (electrical frequency adjust) for the LPRO 101 is given as +/- 1.5 E -9 which for the 0 to 5 volt tuning range covers a +/- 15mHz tuning range (in volts per Hz tuning rate, this equates to ~167 volts per Hz). IOW, the tuning requirement of the AR60A is a gross mismatch to what the gpsdo is expecting.

 First thing you need to do is compare its output against another reference such as a gpsdo using an oscilloscope so you can test whether it can be adjusted using the external frequency adjust pin connection (and the internal trimpot if it has one - the manual implies it doesn't when the external frequency adjust option is installed/enabled (it's probably there regardless of what that poorly written manual implies though).

 The priority for you is to ascertain whether it's even possible to adjust the frequency electrically through that freq adj connection. If not, then it's game over as far as you're concerned unless you can find a way to modify it to re-enable this "option".

[daddioo]

Thanks for the reply, I will do more tests if I get a good result I will let you know.

[TomD]

Hello Vindoline,
thank you for your great PCB setup. I ordered some PCBs and install the HW. I use the FW 0.06c but I have a issue. As long as I didn't 'activate' the BMP280/AHT20 the device run well, but when the BMP/AMP20 is 'defined' I got just the header line on the OLED. Can you please advice how you get the OLED and the BMP280/AHT20 (the small sensor on a mini PCB) running at the same time? Did you redefine the connection for the sensor /or use I2C and SPI?

Please support. Many Thannks in advance.

Again thank you for the great set-up/PCB.

[daddioo]

Hello everyone, today a strange thing happened to the GPSDO v0.06c, everything was working ok, suddenly the display screen became all white, but I noticed that the gpsdo continues to work I checked with the Terminal with the mobile phone, I ask if it is possible to add a button in the code for a display reflash without resetting everything every time, the display used is ILI9341.
Thanks, Giuseppe

[vindoline]

Hello Vindoline,
thank you for your great PCB setup. I ordered some PCBs and install the HW. I use the FW 0.06c but I have a issue. As long as I didn't 'activate' the BMP280/AHT20 the device run well, but when the BMP/AMP20 is 'defined' I got just the header line on the OLED. Can you please advice how you get the OLED and the BMP280/AHT20 (the small sensor on a mini PCB) running at the same time? Did you redefine the connection for the sensor /or use I2C and SPI?

Please support. Many Thannks in advance.

Again thank you for the great set-up/PCB.

Hi Tom, I'm sorry it took so long to respond - I'm just seeing this message today.
First off, I'm just a keen hobbyist, not an engineer. And I am DEFINITELY not a software guy.
I looked at the code, and my BMP280 is defined as I2C. I don't remember having any difficulty with the BMP280, but I probably had to go into the software and un-comment some code blocks to activate it.
I do remember that it took me a really long time to figure out how to talk to the unit with the Arduino software that I use. I think it was several days of playing around to get it to work.
If you are having trouble, I would suspect that it is an I2C address conflict or that the BMP280 board is bad.
If you're still having trouble, I would recommend reaching out to Andrew - he has been really helpful and knows his software inside out!

[TomD]

Thank you Vindoline, I will try to fix the possible I2C address problem. Thank you again

[Sergii]

Hello, everyone!
Thank you for the excellent project. Based on the comments in the BUG LIST from uflex, I fixed most of the bugs directly in the gerbers:
FIXED: 1. Increase the footprint of C32 (MLCC) from 0603 to 0805. 
FIXED: 2. Footprint C39 (MLCC) 0603 should be increased to 0805 for KEMET C0805C102J5GACTU. 
FIXED: 4. **CRITICAL BUG:** Unintended connection between the wiper of P1 (Balance) and the non-inverting input of U2. 
FIXED: 5. The ‘GAIN’ and ‘BALANCE’ labels on the PCB are swapped. 
FIXED: 7. The nRST line capacitor to GND is missing in the layout but not used anyway because of the following: The MCU reset needs to occur relatively slowly to allow enough time for the OCXO to stabilize. To address this, resistor R58 (47k/0603) has been added from nRST to Vcc, and MLCC C51 (10uF/0805) from nRST to GND. The resistor ensures the capacitor discharges quickly enough for immediate restart after power-off. A reverse diode across R58 and a smaller capacitor for C51 could also be considered as alternatives. 
FIXED: 8. The uP-clock from the 74ACT04 is 5Vtt. Although STM32 OSC_IN is 5V tolerant, a voltage divider of 1k8 - 3k3 has been added to prevent clipping against the internal diodes in the STM32 and avoid distortion/ringing, bringing the max voltage to around 3.2V. In the current layout, the 1k8 resistor (R60) replaces C36. The 3k3 resistor (R61) has been improvised and placed to the ground of a nearby MLCC. 
FIXED: 11. Additional decoupling MLCC's at 3V3 around the STM32 chip.

The result is pcb version 1.1, which is now fully ready to order from JLC. (what I have already done)

[Shadback]

Hi, so recently I decided to build my own GPSDO project since I'm very interested in building one now my idea was to use lars design with the 4046 but for someone without a lot of background there is a lot I don't know.
in my project I'm using:
STM32H723ZGT6
GPS ZED-F9T Module
AOCJY-10.000MHZ-F-T VCOCXO
and the lars GPSDO PLL using HC390 and 74HC4046
questions:
1. my gps module has a 3.3V PPS output as well as my OCXO I am using the 4046 with a 3.3 vcc i know it is possible but im worried because the RC value would change and unlike lars i cant use lower voltage reference with my STM...
2. I have tried to read lars files and code but it is still not enough is there a good explanation of his PID somewhere?
3.in lars project he used his Arduino to count 5MHz now in my STM i want to count the original 10MHz but I don't understand it well enough can it count without interrupts as an external clock?

Hope you can help...

[lucido]

Hi everyone.

After a bit of work, I managed to get it working.
Thanks, AndrewBCN
Thanks daddioo

Happy gpsdo.

lucido

[lucido]

Good morning everyone.
A small update! I replaced the Ublox M8N GPS receiver with a Ublox Lea-6T. I'm waiting for the Ublox M8T to arrive. I want to see how it works with GPSDO. I added the Bluetooth module. With Android, it works without problems with the Serial Bluetooth app. With Windows 11, it gives me problems, but I think it's a driver issue. Regarding stability, it's excellent, even though I don't have the right tools to measure it. The accuracy isn't bad, as you can see from the frequency counter. As for the oscillator, I'm using a Toyocom TCO-627VC. It works properly, you can find it on eBay. I'd say the whole system is working fine!
Let's keep this interesting post alive.
Greetings everyone.
Happy GPSDO.
lucido